In petroleum-chemical industry, sulfuric acid and hydrofluoric acid catalysts are widely used in the process of isoparaffin-olefin alkylation, especially for light isoparaffin and light olefin alkylation, in order to produce higher molecular weight paraffin with high octane rating, as valuable gasoline blending components. However, both sulfuric acid and hydrofluoric acid share inherent drawbacks including equipment corrosion problem, serious environment and safety concerns. A lot of efforts have been made to develop solid acid alkylation catalysts for substitution of sulfuric acid and hydrofluoric acid.
In recent years, new solid acid catalysts for the above alkylation process have been widely investigated and reported. For example, U.S. Pat. No. 3,549,557, U.S. Pat. No. 3,644,565, U.S. Pat. No. 3,647,916, U.S. Pat. No. 3,917,738 and U.S. Pat. No. 4,384,161 discloses catalysts having molecule sieve as active components. JP 01, 245, 853, U.S. Pat. No. 3,962,133 and U.S. Pat. No. 4,116,880, GB 1,432,720 and GB 1,389,237 disclose SO.sub.4.sup.2- enhanced super acid catalysts; EP 0,433,954, U.S. Pat. No. 3,678,120, U.S. Pat. No. 3,852,371, and U.S. Pat. No. 3,855,342, WO 94/24075 disclose liquid super acid or supported Lewis acid catalyst etc.. But the deactivation of the above molecular sieve catalysts and solid super active acid catalysts occurs quickly, in a few hours or even less than an hour the olefin conversion reduces dramatically. Besides, the product distributions are not ideal and the problems of halide loosing and equipment corrosion exist with the liquid super acid or supported Lewis acid catalysts.
WO 94/03415 discloses a paraffin-olefin alkylation process comprising contacting an olefin-containing feed with an isoparaffin-containing feed in the presence of a crystalline microporous material under conversion conditions of alkylation, including a temperature at least equal to/or above the critical temperature of said principal component of the feed and a pressure at least equal to/or above the critical pressure of said principal component of the feed. Said zeolites include ZSM series, offretite, MCM, mordenite, REY etc.; said layered material includes layered silicate, layered clays etc.. For example, higher olefin conversion and improved catalyst activity and stability can be obtained with MCM series zeolite catalyst. However, the butene conversion is still quite low, only 86.3-99.4 wt %.
CN 1,125,639A discloses an isobutane-butene alkylation process comprising dissolving H.sub.3 PW.sub.12 O.sub.40, H.sub.3 PMo.sub.12 O.sub.40, H.sub.4 SiW.sub.12 O.sub.40, H.sub.k PW.sub.12 Mo.sub.12-n O.sub.40 (n=1-11) etc. heteropoly acids in light fatty acid, ester, ketone, ether, alcohol or the mixture of fatty acid and fatty alcohol with a concentration of 10-70% to be used as catalyst; the catalytic isobutane-butene alkylation reaction is carried out at 10-70.degree. C. with a paraffin/olefin ratio 1.5-18. Although the equipment corrosion caused by H.sub.2 SO.sub.4 or HF is avoided, new problem of separating the reaction products from solvent occurs since the reaction is carried out in the liquid phase. Besides, the olefin conversion and the yield of alkylates are relatively low as shown in the Comparative Examples 1-9, the yield of alkylates is only 0.693-1.736 (based on olefin weight) in the batch reactor.
CN 1,125,640A discloses an isobutane-butene alkylation process. The catalyst used in said process is alkali or ammonium salt of heteropoly acid, such as that of phosphorus-tungsten heteropoly acid, phosphorus-molybdenum heteropoly acid, silicon-tungsten heteropoly acid, silicon-molybdenum heteropoly acid; the alkali or ammonium cation range (mole) for phosphorus series is 0.5-3.0, and for silicon series is 0.5-4.0; the reaction temperature is 30.degree. C.; the ratio of isobutane to butene is 15:1. The yield of alkylates is still quite low for said process and the stability of the catalyst activity is not ideal. As in the example, the highest alkylates yield of said alkylation process in batch reactor is 1.854 (based on olefin weight), and the activity reduces with the increase of the reaction times. In said Example 1, the alkylation reaction was carried out in the presence of Cs.sub.2.5 H.sub.0.5 PW.sub.12 catalyst, 0.4378 g olefin and paraffin with a paraffin/olefin ratio of 15 were added to the reactor and reacted at 30.degree. C. for 2 hours; 0.8118 g alkylate oil was obtained with the yield of 1.854. After separating the catalyst and dried at 100.degree. C. for 2 hours the catalyst is reused under the same conditions and the alkylate yield is reduced to 1.384.
U.S. Pat. No. 5,324,881 discloses a process for isoparaffin-olefin alkylation in the presence of a supported heteropoly acid catalyst. Said heteropoly acid contains at least one central element selected from the group consisting of: P, Si, B, Ge, As, Se, Ti, Zr, Mn, F, V, Ce, Th, and at least one coordinating element selected from the group consisting of: Mo, W, V, Mn, Co, Ni, Cu, Zn, Fe. The catalyst used for said process is a supported heteropoly acid catalyst, according to the Example report, all the heteropoly acid catalysts were pretreated above 350.degree. C., the olefin conversion was up to 87 wt % and the highest C.sub.6.sup.4 alkylates yield was at most 1.4 g/g2C.sub.4.sup.-. It is proved that the stability of the catalyst activity is still not promising by said process.